Lets use this example.
Product total amount is $300
Minimum manual payment amount is set to $60
I go to the Cart and enter $30
Then proceed to the checkout and 'PLACE ORDER'
I will not be able to place the order as the minimum amount l need to enter is $60
Please ensure that customers can access the cart page again quite easily to enter the minimum manual payment amount or above this amount, for the transaction to be successful.